1. Field of the Invention
This invention relates in general to ethanol production processes, and more particularly to ethanol production processes having enhanced value products produced from the whole stillage and/or reduced volatile organic compounds (VOC) emissions from the process.
2. Prior Art
In a conventional ethanol production process utilizing corn as the starch containing feedstock, the corn is ground to produce a milled corn. This is typically achieved by the use of a hammer mill or other similar conventional milling equipment Water and enzymes are added to the milled corn and heated to form a liquefied mash. The liquefied mash is then mixed in a fermentation vessel with water, yeast and selected minerals and nutrients to enhance the fermentation of the mash. The fermented product, commonly referred to as the “beer”, is then distilled to produce an ethanol rich stream (about 95% ethanol and 5% water by weight) and a whole stillage. The whole stillage comprises water, as well as the solids resulting from the fermentation. It is typical to centrifuge the whole stillage to remove a substantial portion of the water to form a wet distillers grain. The wet distillers grain includes most of the protein containing solids that is found in the whole stillage. The removed water containing nutrients and other solids generally known as the thin stillage is sent to an evaporator to remove a substantial portion of the water. The remaining nutrients and solids called the syrup are then combined with the wet distillers grain. The combined syrup and wet distillers grain is sent to a dryer to produce a dry protein containing animal feed called distiller dried grain solubles (DDGS).
These prior art ethanol processes have several significant problems. One problem is the energy costs to remove the water from the whole stillage to produce a low economic value DDGS. A second problem is the environmentally unacceptable amount of VOC's, air toxics, and combustion pollutants, such as CO, NOx, and particulate matter, released into the atmosphere during the drying process. To achieve an acceptable VOC, air toxics, and combustion pollutants release amount requires large capital investments in thermal oxidizers and other equipment to capture the VOC, air toxics, and combustion pollutants released during the drying process, as well as expensive annual equipment maintenance. These problems have hampered the commercial success of ethanol production processes that have to date remained economically viable due only to governmental subsidies.